1. Field of the Invention
The present invention generally relates to the fabrication of microscale structures, such as structures and devices for microelectronics applications. More particularly, this invention relates to a method of forming extruded structures by initiating selective grain growth in polycrystalline materials, and devices with such structures for use in microelectronics applications.
2. Description of the Prior Art
In the past, conventional lithographic techniques have been used to produce various structural features, such as metal pads and lines for microelectronic applications. While lithographic techniques are widely and successfully used in the art, nano-scale features (i.e., operative structures and components that have a controlled dimension of less than ten nanometers) are difficult to form by conventional lithography. In view of the demand for greater miniaturization of microcircuits and their components, it would be desirable if a method were available that enabled the patterning of metallization to form nano-scale features. In addition to metal pads for microelectronic applications, a wide variety of electronic components and devices could benefit or utilize nano-scale features, including digital recording media.
The present invention provides a method of forming extruded structures from a polycrystalline material and structures formed thereby. A key aspect of the invention is the determination of the mechanism by which selective grain growth can be induced and controlled in a polycrystalline material that is constrained in all but one direction. This mechanism is believed to involve the growth of grains that have been formed by patterning and/or appropriate deposition techniques to have fewer than six grain boundaries, six grain boundaries being the most thermodynamically stable grain structure. If sufficiently heated, those grains located at a patterned surface of the polycrystalline material and having fewer than six boundaries will undergo grain growth in a direction normal to the patterned surface. If constrained during heating, as is the case if all but the patterned surface of the polycrystalline material contacts and is contained by a second material with a lower coefficient of thermal expansion (CTE), compressive stresses induced by the second material will cause this grain growth to be predominantly outward and normal to the patterned surface of the polycrystalline material.
In view of the above, the method of this invention generally entails forming a structure that comprises a polycrystalline material constrained by a constraining material in all but one direction, with the polycrystalline material having a surface that is normal to the one direction. The polycrystalline material is then selectively heated, during which the constraining material restricts thermal expansion of the polycrystalline material in all but the one direction normal to the surface of the polycrystalline material. As a result, stresses are induced in the polycrystalline material that lead to grain growth from the surface of the polycrystalline material in the one direction. The growth of an individual grain produces an extruded structure that projects above the surface of the polycrystalline material. Sufficient grain growth can occur to produce extruded structures which are, based on an average grain size of, for example, about four xcexcm, nano-scale structures on the surface of the polycrystalline material. (As defined herein, nano-scale designates a structure with at least one dimension that is less than ten nanometers.) When appropriately configured, nano-scale structures formed in accordance with this invention can be an operative component of a wide variety of devices, including digital recording media.
Other objects and advantages of this invention will be better appreciated from the following detailed description.